Crosslinking agents based on amino resins and coating compositions made with these are well known in the art and have been used for more than half a century in diverse applications including general industrial coatings, automotive coatings, coil coatings, powder coatings, baking enamels, and wood finishes. These crosslinking agents are based on reaction products of aldehydes, usually formaldehyde, with amine, amide, urethane or amidine compounds (together referred to as aminoplast formers) such as melamine, guanamines, urea, and substituted ureas. Among the major drawbacks of coatings based on these amino resins are formaldehyde emissions during cure.
Various crosslinking compositions have been developed that are based on combinations of aminoplast formers and aldehydes other than formaldehyde. Many of these are either less efficient or more expensive than the known formaldehyde-based systems, or are otherwise objectionable from a safety and health view. Despite numerous efforts made, none of the crosslinker resins proposed has yet found wide market acceptance. A reaction product of a cyclic alkyleneurea and glyoxal when combined with polyfunctional hydroxy and/or carboxyl group containing materials offers good crosslinking already at low (ambient=23° C.) temperature, see WO 2009/073836 A1.
It is an object of this invention to provide crosslinking compositions based on reaction products of cyclic alkyleneureas and multifunctional aldehydes that have application properties that can be tailored to the intended use, and that are either on par with the known formaldehyde based systems, or at least provide a favourable match to these known systems.